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MatPlus.Net Forum Retro/Math [Original] Noel Junio, How many legal last moves?

### [Original] Noel Junio, How many legal last moves?

I have received an e-mail with request for publication of an original problem on MatPlus Forum, which after confirmation I do here:

QUOTE
I'm Noel Junio from the Philippines. I compose problems during my leisure.

(= 8+1 )

Noel F. Junio (Philippines)
Original
Count every possible legal and specific one last move of
white.
How many and what?
A. Diagram
B. Bg1->b6:

Solutions:

A. Only one possible legal and specific last move of white: 1.b7xSa8=B#

It is neither of the following because there’s no last legal move of black.

1.b7xBa8=B#?
1.b7xRa8=B#?
1.b7xQa8=B#?
1.b7-b8=Q disc#?
1.c6-c7 disc#?
1.d5-d6 disc#?
1.c5xd6 e.p.#?
1.e5xd6 e.p.#?

Black's last move was 1...Sb6(x)a8

B. 9! (7+2)

1.b7xSa8=B#
1.b7xBa8=B#
1.b7xRa8=B#
1.b7xQa8=B#
1.b7-b8=Q disc#
1.c6-c7 disc#
1.d5-d6 disc#

If black's last move was 1...Kg1(xS/B)h1 in response to 0.Sd4(x)e2++ or 0.Sd4(x)e2+ if there's a white
pawn on c5.

and

1.c5xd6 e.p.#
1.e5xd6 e.p.#

If black's last move was 1...d7-d5 in response to various white's last move. For example, 0.c6-c7 disc+ or
0.e4-e5 disc+ or 0.b7xa8=B+ et cetera.

(Mark the invisible text to read the solution. SH)

It seems that -1.c5xPd6 e.p. or -1.e5xPd6 e.p. (followed by -1...d7-d5 and then -2.b7xSa8=B+) are also legal last moves in A.

QUOTE
On 10/12/2015 8:07 AM, Noel Junio wrote:
> Yes, Mr. Prentos was correct. So what's the best to do now? Shall we remove the pawn d6 in A and B? So that the answer is 1 in A and 6 in B or just leave it that way so that the answer in A is 3! and the answer in B is 9!
>
> Please send my thanks to Kostas Prentos.

QUOTE
On 10/12/2015 1:47 PM, Noel Junio wrote:
> It is best to retain the diagram as it is. I just want to correct my solution in A. It should now be 3, indicating the 2 en passant capture seen by Sir Kostas Prentos. I believe this is correct now.
>
> Thank you.

Personally I will forget Part B, remove Pawn d6 and make the stipulation "Last move?" - of course it might be anticipated but would be a good effort from a newcomer.

(5) Posted by Guus Rol [Tuesday, Dec 1, 2020 00:03]

It's not a big problem but let's give it a "nice" mark. Here is my version.

(after Noel Junio) Which specific retraction moves can be identified?
(= 14+1 )